Although the present invention is contemplated to be applicable to any type flow measuring device, the description below will be made with reference to the operation of a Coriolis type mass flow meter. Coriolis type mass flow meters operate on the principle that a fluent material passing through a conduit or tubing, when exposed to a deflection or oscillation transverse to the direction of flow, will react with a measurable force (the Coriolis force) on the walls of the tubing. The Coriolis reaction force is generated by the material moving in an instantaneously changing curvilinear path and is directly proportional to the momentum of the material in the tubing. The Coriolis force is directed against the tubing in the opposite direction of the deflection of the flow tube on the inlet side of the deflection and with an equal and oppositely directed force on the outlet side thereof. The measurement of this reaction is used to determine the mass flow rate passing through the flow tube.
Various oscillation techniques have been employed within Coriolis mass flow meters. Certain techniques are described in U.S. Pat. No. 5,115,683 to Wayne Pratt which issued on May 26, 1992. This '683 patent (commonly assigned with the present invention) is herein incorporated by reference.
Because of the range of sensitivity of a Coriolis mass flow meter, various size tubing is utilized in order to accommodate various flow rates. For example, ABB K-Flow, Inc., the assignee of the present invention, produces a range of flow meters which are applicable to various flow rates. The selection of a specific flow meter will depend upon the operational parameters of the process and the fluid stream in which the meter is to be placed. Preferably, the least expensive meter for a particular application is selected by the purchaser. The present invention contemplates the use of relatively small meters to measure flows normally outside their maximum range of accuracy.